1. Field of the Invention
This invention relates in general to fan coil units. More particularly this invention concerns a heat transfer unit including a fan for circulating the air in heat exchange relation with a heat exchanger.
2. Prior Art
In a conventional residential split system air conditioning unit the condenser of the refrigeration circuit is located exterior of the residence. Typically, this unit has a condensing coil, a fan for circulating outdoor ambient air over the condensing coil and may additionally have a compressor, reversing valves and various controls. The residential split system further includes an indoor unit having an evaporator for transferring heat energy from the indoor air to be conditioned to the refrigerant flowing through the evaporator and a fan for circulating the indoor air in heat exchange relation with the evaporator. This type of unit is referred to as a fan coil unit.
Generally, when a heat exchanger is used to effect cooling of air the heat exchanger will be connected to a source of a relatively cold fluid medium such as water or to a source of suitable refrigerant capable of changing state from liquid to a gas to absorb heat energy. The air to be cooled is routed over the heat exchanger in heat transfer relation with the relatively cold fluid media. This relative cold medium absorbs heat energy from the air thereby cooling the air to the desired temperature level. Oftentimes, the air is cooled below its dew point such that condensate collects on the surfaces of the heat exchanger. In a plate fin heat exchanger these surfaces are primarily the fins mounted to the tubes defining a fluid path for the refrigerant.
If the condensate falls randomly throughout the heat exchange assembly this may result in puddles of condensate forming at various locations within the unit. These puddles of condensate not only provide unwanted moisture within the unit but also serve to provide a catalyst for increasing corrosion and may create other problems in the unit. Many methods of collecting and diverting this condensate have been used.
One method of attacking the problem of condensate collecting throughout the unit is to mount the heat exchanger at a sufficient angle to horizontal that the weight of the condensate will cause the condensate droplets to flow along the axial length of the fins of the heat exchanger into condensate collection means. Hence, the condensate will not drip randomly from the coil but will flow along the axial length of the fin toward a condensate collection pan. Then the condensate may be drained from the unit from a single collection area.
Another approach to the condensate problem is to provide a fin surface having ridges and grooves designed to direct collected condensate along the axial length of the fin when the heat exchanger is mounted at an angle insufficient for the mere weight of the condensate to cause the condensate to flow along the fin. U.S. Pat. No. 3,902,551 discloses such a fin arrangement wherein the fin includes channels for conducting collected condensate to the condensate collection area.
As is known in the art, it has been found that a wavy fin surface is advantageous for promoting heat transfer between the air flowing through the heat exchanger and the cooling medium flowing through the tubes connected to the fins. This wavy surface forces a turbulent type air flow through the heat exchanger causing the air to be mixed and acts to promote heat transfer between the air and the fin surfaces while causing a minimum of pressure drop in the air flowing therethrough.
It has additionally been found that one of the highly efficient ways of circulating air through a heat exchanger is to cause the air to be blown through the heat exchanger utilizing a centrifugal fan. To reduce the pressure drop or flow resistance of the air flowing through the heat exchanger and to create an advantageous velocity profile across the heat exchanger, it has been found that mounting the heat exchanger horizontally across the air flow path or close to horizontally, and spaced from the fan discharge both reduces the overall flow resistance of the heat exchanger and allows for a desirable velocity profile. Naturally, when mounting a heat exchanger within a particular size casing, the maximum possible length of the heat exchanger is less when mounted horizontally than it would be if the heat exchanger was mounted at an angle to the horizontal. Hence, a heat exchanger mounted at a small angle to horizontal is found to be more efficient in terms of the size of the heat exchanger and the pressure drop of air flowing therethrough. The combination of mounting the heat exchanger at relatively small angle to horizontal as well as using a wavy type fin in the heat exchanger serves to promote a highly efficient heat exchanger with a minimum pressure drop. It has further been found that by mounting the blower below the heat exchanger such that air is blown through the heat exchanger that the fan scroll for the blower may be designed to optimize fan performance.
When the fan is mounted above the heat exchanger such that it is a draw-through heat exchanger, the fan scroll typically is arranged to direct the air from the unit into a duct. Under these circumstances, the fan scroll outlet is typically sized as a compromise between optimum for air flow purposes and what is necessary for duct purposes. Hence, aerodynamic inefficiencies may occur. By mounting the fan below the heat exchanger, the outlet of the fan coil unit may be appropriately sized to the duct work to minimize aerodynamic inefficiencies.
By the combination of utilizing a centrifugal fan located to blow air through the indoor heat exchanger, said indoor heat exchanger including a wavy type fin, the indoor heat exchanger being mounted at an angle substantially close to horizontal, and utilizing an outlet from a fan coil unit designed to match with the duct work to minimize aerodynamic inefficiencies it has been found that the watts consumed by the electric motor driving the fan per thousand cubic feet of air delivered can be reduced substantially in half from the fan watts utilized in present commercially available fan coil units. This reduction in fan watts reduces the total energy consumed by an air conditioning system to transfer a given amount of heat energy to effect cooling thereby increasing the efficiency of the unit.
When the heat exchanger is mounted at a low angle to horizontal and includes no channels for directing condensate along the axial length of the fins then the condensate will drip substantially across the entire heat exchanger surface. The herein application discloses a combination fan deck and condensate collection pan extending across the unit to receive the condensate dripping from the unit. Additionally, condensate will drip through a fan scroll opening in the combination fan deck and condensate pan and into the fan scroll wherein the squirrel cage rotor of the centrifugal fan is located. During operation of the unit the air flow from the fan will serve to prevent condensate from dripping into the fan and will tend to force any collected condensate from the fan scroll. There has additionally been provided a drain collection system for collecting condensate from the condensate pan. This drain collection system also includes means for collecting condensate from the bottom of the fan scroll which may accumulate when the fan is not operating. Hence, any problems of collected condensate causing corrosion or forming pools in unwanted areas are avoided by the utilization of a combination collection means to divert condensate from both the combination condensate pan and fan deck and the fan scroll.